In the new film “Margin Call,” to be released on Oct. 21, Academy Award-winning actor Kevin Spacey plays Sam Rogers, the deeply conflicted trading floor manager at a Wall Street investment firm. The movie, which, despite having a low budget of $3.4 million boasts an all-star ensemble cast including Mr. Spacey, Jeremy Irons, Paul Bettany, Demi Moore, Stanley Tucci and Zachary Quinto, zeroes in on a group of executives grappling with the moral price of the actions required to save the firm from collapse: notably, selling off billions in mortgage-backed securities in a single day.

Rogers may be gruff and moody, but unlike some of the business types that Mr. Spacey has played in previous films—like John Williamson in “Glengarry Glen Ross” for example—he’s got a heart. Sure, he’s probably part of the much-maligned 1%, but Rogers nevertheless needs his job. “He probably doesn’t have as much money as he used to, if you break it down: He’s divorced from his wife. She got the house. He’s living somewhere else,” said Mr. Spacey from Ibiza earlier this month, where he was promoting the film. (His character also has a dog with cancer: “I’m paying almost a thousand bucks a day to keep her alive,” Rogers reveals in an opening sequence.)

When Mr. Spacey read the script for “Margin Call” last year, he said he saw an opportunity to “personalize and humanize” the people who were being vilified for destroying the global economy. He and the other actors involved in the film liked first-time director J.C. Chandor’s screenplay so much that they agreed to take salaries that were “peanuts” compared to what they normally receive, says co-producer Neal Dodson, who is a partner with Mr. Quinto at Before the Door Pictures.

Below, an edited transcript of an interview with Mr. Spacey.

The Wall Street Journal: This film is by a first time director and screenwriter, J.C. Chandor, and it’s a pretty low budget movie compared to what you usually do. When you think back to that time when you read the script, what exactly was it that made you think, “Yes, this is it. I am going to take a chance on this.”

Kevin Spacey: The truth is I have been doing that my whole life…. If you go back and look at my early work, much of it was with first-time directors like Sam Mendes who had a great theatrical career and who I knew was an incredible visual stylist. I never ever judge somebody on the number of their credits. What I judge them on is their intelligence, their grasp of the material. And the conversations that J.C. and I had were wonderful.

How did the script get to you in the first place?

I had gotten to know Zachary [Quinto, an actor and co-producer of the film], because he had come to London see “Inherit the Wind” and we became friends. Months later he said he was going to produce his first movie and knowing what that’s like I wanted to be as supportive as I could. Reading the script it just genuinely felt to me that it was such a personal story and it was it was done in such a way that it was like a ticking clock… What I liked about the film is that every time you think you’ve met the top person, the hierarchy gets bigger and then you meet another person. And then, it’s like “Oh no that’s the guy.” Then “No, that’s the guy.” It shows you that so many people in the banking world are following orders and weren’t these big CEOs making gallons of money but are people who have tried to do an honest job. Everyone got thrown in this you’re-all-shit-bags barrel.

When did you sign on?

It was early to mid spring…I was the first actor in after Zachary. And literally as we were getting closer and closer to shooting more and more actors came on board. Jeremy [Irons] was the last. I had been shooting and then I had to fly back to London for a big benefit we did with Paul McCartney for the Old Vic [Theatre, in London, where he serves as artistic director]. And Jeremy and Sinead [Cusack, his wife] came that night. He had been offered the role that morning and I pinned him up against the wall and said “you’ve got to do it.” They had to get him a visa in like three days. I think there’s a credit at the end of the movie that says “Thanks to the Jeremy Irons Miracle Visa Team.”

Humanizing bankers, some might argue, is an unusual pursuit at this moment in time, when people are occupying Wall Street. Do you think that this movie might change people’s opinions about Wall Street types?

I am sure speaking for the bankers it would be great if people took a second look. I think that sometimes we get caught up in wanted to blame and point fingers and wanting to understand. Did people fulfill their responsibilities? And are certain people crooks? Without question it’s very easy to come up with simple answers to very complicated situations…and it gives people some level of comfort to say “that’s a f—ing bastard.” But at the end of the day we’re all human beings.

You went to Citigroup and talked to some executives, right? What sorts of things did you talk about to help you get into the mindset of someone like Sam Rogers?

I met a lot of guys who work on the floor and were really stunned by the things being said about bankers in general. Yes [I went to Citigroup]. But I also know a lot of bankers, and I spent time doing one-on-one research with bankers who do what my character did.

Anybody you could name?

I like to keep my sources to myself.

What kind of stories did you ask people to tell you to get your head around this Sam Rogers character?

Well, I wanted to understand how does someone have that many people under them? Who are their right hand- and left hand men and women? What kind of salary are you making? I kept thinking, “What would it feel like if you knew something nobody else knew?” You had to go to your local bar with your friends, go to a wedding with your wife…and you know something is about to happen in the world financially that’s going to change everybody’s life. How do you live with that?

What did they say?

They said it was terrible. What I tried to do, at the very beginning of the film when Sam [Rogers] has to come out and give this kind of pep rally, this kind of well “You’re all here because you’re better than those guys” speech. He had to be matter of fact and positive even though there’s just been a bloodbath. I found that to be such an interesting piece of writing.

I think unlike some of the other actors, you have experience playing business types…the pace of the dialogue reminded me of David Mamet’s “Glengarry Glen Ross.” Did you see any similarities to this script and Mamet?

I didn’t see any similarities in the role I played. But I did feel at some point—once I decided on the look I wanted to have, and I was standing there before we started shooting—I thought, “Wow, actually this is the kind of part that Jack Lemmon would have played in his 60s.” And it’s not the [John] Williamson role who was a real a–hole and didn’t give a s— about the guys who worked under him and thought everyone was replaceable. I felt [Sam Rogers] was like an everyman. I felt like I was not in the same circumstances but I just remembered Jack so fondly in that film and thought he influenced me in this one.

Simon Baker said that he tried on the suit the costume department provided, but felt that his character would wear a bespoke suit—so he brought in one of his own. Was there anything you did, sartorially, to make your character more convincing?

Well I knew I decided on suspenders at the costume fitting. I liked it was the kind of thing you see an older guy do. My wig guy in London made this fantastic piece that just aged me in the right way. We weren’t that far from shooting when I said I was going to do this film…. They get immediately nervous and think, “Oh f—, he’s going to put a horrible wig on his head.” So there’s a panic that starts with producers. I said “This guy’s fantastic. He’s made tons of pieces for me for the theater.” Often I will take a picture of someone—it might be someone just sitting in a restaurant—and I will give Campbell [the wig stylist] that photo and say “Make me that.” And he does. And he’s brilliant. But until you get it on your head and it is coiffed people aren’t so sure.

I know we’re dealing with two very different types of movies here, but “Horrible Bosses,” in which you starred this summer, presents a very different perspective on corporate America than “Margin Call” does. Could you talk about that?

“Horrible Bosses” I thought was a very funny film and I thought if the three guys [Charlie Day, Jason Sudeikis and Jason Bateman] have chemistry then the movie’s going to work. And if they don’t then the movie won’t work. [“Horrible Bosses”] was not the kind of movie where we are setting out to say anything about the world…to me it was another version of “Nine to Five.” Having just come off of doing “Margin Call” playing a real person with real problems and dilemmas—they were just two entirely different experiences.

About Speakeasy

Speakeasy is a blog covering media, entertainment, celebrity and the arts. The publication is produced by Barbara Chai and Jonathan Welsh with contributions from the Wall Street Journal staff and others. Write to us at speakeasy@wsj.com or follow us on Twitter at @WSJSpeakeasy or individually @barbarachai.